Two key topics of many second-year organic chemistry courses are substitution and elimination reactions. Predicting and explaining substitution and elimination reactions tends to be a challenging task for students, as documented in the research literature. Motivated by the many documented challenges experienced by students when learning these reaction types, we developed an adaptive intervention designed to improve student explanations of an S[subscript N]1 reaction mechanism. The intervention relies on computer-based scoring to evaluate students' written explanations of a reaction mechanism (i.e., preassessment) in determining which of two tutorials to present to a respondent. Tutorials were designed to facilitate construction of explanations of the given S[subscript N]1 reaction mechanism based on known student difficulties with reaction mechanisms and recommendations for teaching S[subscript N]1-related concepts in the chemical education research literature. The Level 1 tutorial aims to move students from a description only explanation to a surface level explanation (i.e., Level 2). The Level 2 Tutorial aims to move students from a surface level explanation to a deeper level explanation (i.e., Level 3). Success of the intervention was evaluated through ordinal logistic regression, finding that the Level 1 Tutorial and the Level 2 Tutorial are net effective, with odds ratios of 2.46 and 1.73, respectively, in increasing students' level of explanation sophistication.